Long before we can build something for real, we know how it will work and what it will require by way of materials and design. The steampunk genre gorges on Victorian designs for steam-powered helicopters (yes, there were such things) and the like, with films such as Hugo (2011) and gaming apps such as 80 Days (2014) telescoping the hard business of materials science into the twinkling of a mad professor’s eye. Always, our imaginations run ahead of our physical abilities.

At the same time, science fiction is not at all naive, and almost all of it is about why our dreams of transcendence through technology fail: why the machine goes wrong, or works towards an unforeseen (sometimes catastrophic) end. Blade Runner (1982) didn’t so much inspire the current deluge of in-yer-face urban advertising as realise our worst nightmares about it. Short Circuit (1986) knew what was wrong with robotic warfare long before the first Predator aircraft took to the skies.

So yes, science fiction enters clad in the motley of costume drama: polished, chromed, complete, not infrequently camp. But there’s always a twist, a tear, a weak seam. This genre takes finery from the prop shop and turns it into something vital – a god, a golem, a puzzle, a prison. In science fiction, it matters where you are and how you dress, what you walk on and even what you breathe. All this stuff is contingent, you see. It slips about. It bites.

Sometimes, in this game of “It’s behind you!” less is more. In Alphaville (1965), futuristic secret agent Lemmy Caution explores the streets of a distant space city, yet there is no set dressing to Alphaville: it is all dialogue, all cut – nothing more than a rhetorical veil cast over contemporary Paris.

More usually, you’ll grab whatever’s to hand – tinsel and Panstick and old gorilla costumes. Two years old by 1965, at least by Earth’s reckoning, William Hartnell’s Time Lord was tearing up the set of Doctor Who and would, in other bodies and other voices, go on tearing up, tearing down and tearing through his fans’ expectations for the next 24 years, production values be damned.

Bigger than its machinery, bigger even than its protagonist, Doctor Who was, in that first, long outing, never in any sense realistic, and that was its strength. You never knew where you’d end up next: a comedy, a horror flick or a Western-style showdown. The Doctor’s sonic screwdriver was the whole point. It said, we’re bolting this together as we go along.

What hostile critics say is true, in that science fiction sometimes is more about the machines than about the people. Metropolis (1927) director Fritz Lang wanted a real rocket launch for the premiere of Frau im Mond (1929) and roped in no less a physicist than Hermann Oberth to build it for him. When his 1.8-metre-tall liquid-propellant rocket came to nought, Oberth set about building a rocket 11 metres tall powered by liquid oxygen. They were going to launch it from the roof of the cinema. Luckily, they ran out of money.

The technocratic ideal may seem sterile now, but its promise was compelling: that we’d all live lives of ease and happiness in space, the moon or Mars, watched over by loving machines – the Robinson family’s stalwart Robot B-9 from Lost in Space, perhaps.

Once Star Trek‘s Federation established heaven on Earth (and elsewhere), however, then we hit a sizeable snag. Gene Roddenberry was right to have pitched his show to Desilu Studios as “wagon train to the stars”, for as Dennis Sisterson’s charming silent parody Steam Trek: The moving picture (1994) demonstrates, the moment you actually reach California, the technology that got you there loses its specialness.

If the teleportation device is not the point of your story, then you may as well use a rappelling rope. Why spend your set budget on an impressive-looking telescope? Why not just have your actor point out of the window? The day your show’s props become merely props is the day you’re not making science fiction any more.